The present invention relates to an improved thermal recording method.
Published Japanese Application No. 62-60694 discloses a thermal recording method employing an imaging material of the type described in U.S. Pat. No. 4,399,209. This imaging material includes a layer of photosensitive microcapsules which is carried on a support. The internal phase of the microcapsule includes a photosensitive composition and an image-forming agent and possesses a temperature (the glass transition temperature) above which the composition must be heated before it will react efficiently in the presence of light or ultraviolet radiation.
In accordance with the teachings of Japanese published application No. 62-60694, images are prepared by image-wise heating the aforementioned imaging material while the imaging material is simultaneously exposed to light or ultraviolet radiation. In the areas in which the material is heated, the melting point, softening temperature or glass transition temperature is increased by the exposure as a result of photopolymerization of the internal phase. In areas in which the imaging material is not heated, the simultaneous exposure to light or ultraviolet radiation has little or no effect on the physical characteristics of the internal phase. Accordingly, when the exposed medium is assembled with an image-receiving sheet and heated to a temperature above its original melting, softening or glass transition temperature, the internal phase is released from the microcapsules only in the areas which are not photohardened.
In accordance with one of the embodiments discribed in Japanese Patent No. 62-60694, full color images are obtained using a combination of microcapsules containing different image-forming agents such as cyan, magenta, yellow and black image-forming agents and photohardenable compositions which are principally sensitive to different bands of actinic radiation. In this manner, the imaging material can be image-wise heated using a thermal print head controlled by an image processing signal and the microcapsules containing the different image-forming agents can be selectively hardened as a function of their combined exposure to heat and radiation of the selected wavelength.
The imaging materials described in the Japanese publication are false color systems. For example, in one embodiment, the cyan, magenta, yellow and black producing microcapsules contain photoinitiator systems having light absorption bands of 280-340 nm, 340-380 nm, 380-450 nm and 450-600 nm, respectively.